The temperature of the surface of the cover and, in certain areas, also of the foundation of a road has different influences, particularly of a dangerous or harmful nature. Dangers develop particularly for traffic on roads from different temperatures of adjacent road sections in the area of the melting point of water. Thus, sections of roads running across bridges are exposed to greater temperature fluctuations, especially to a faster cooling than the road sections adjacent to them, which can lead to a local ice formation on the bridge section of the road. One of the objectives of the invention is to warn the approaching motor vehicle driver of such a danger. Those authorized to maintain the roads have, among other duties, the duty of preventing or removing any danger which could arise from the road. This is the reason why the described phenomena is counteracted by distributing salt on the road. However, this is done preventively and amply when a decrease in the temperature is expected below the melting point of the water. The distribution of salt by duration and amount could be calculated more exactly if the temperature development around the freezing point could be observed more exactly and more simply. The salt leads to damage to the road and particularly on bridge structures. The damage increases with the duration of the action of the salt and with its concentration. Therefore, the costs for the necessary maintenance of the bridges depend also on the scope of the salt distribution.